This invention relates generally to a sleep unit such as an inner spring mattress or a box spring mattress support, and more particularly to such unit having an internal plate or frame movable into a position in which portions thereof lie between selected turns of the springs for adjusting the firmness of the sleep unit.
Adjustable inner spring mattresses and box springs are known in which the compressability of the springs are adjusted to thereby adjust the firmness of the sleep unit. Otherwise, a central board may be employed for affecting the firmness of the sleep unit, or a plurality of adjustable tubes are used for adjusting the firmness.